Wireless devices provide connections to multiple wireless networks in multiple and varied frequency bands by means of antenna(s). This requires multiband antennas that can be used in multiple frequency bands. An antenna is a medium for transmitting and receiving electromagnetic waves. These days' consumer wireless handheld devices are getting thinner and more compact; this in turn calls for a size reduction for most of the components including the antenna. On the other hand more and more communication protocols using different frequency bands are being added. As more frequency bands (larger bandwidths) need to be supported, a larger antenna volume is desired. As you can see both the statements above are contradicting and it is a challenge to satisfy all the requirements. However, achieving a wide low band bandwidth separately or in conjunction with an ultra wide high band has been very challenging if not impossible using a passive antenna in the past, especially in ultra slim and small portable wireless devices. Cellular portable devices available in the market today that cover a wide low band bandwidth generally use one of two approaches. One approach uses some type of active solution (e.g., radio frequency (RF) switch, tunable capacitors and so on) to tune the resonance frequency depending on the band usage at a given point. Disadvantages of this solution include added cost and complexity, more discrete components are required, increased complexity from a software perspective, and increased losses in the RF chain.
Another approach is to split the low band section into two antennas (e.g., one at the bottom and one at the top). The antenna at the bottom covers the 850/900 bands and the antenna at the top covers the 700 band). A disadvantage of this solution is that two antennas need more real estate in an already very crowded small portable device. Furthermore, the device is more expensive and complex from the point of having two separate radiators, feeding clips, matching components, coaxial cable, etc. Also, if one of the transmitting antennas is placed at the top of the handset, this might cause specific absorption rate (SAR) issues that may be very hard to resolve.
Therefore, there is an opportunity to develop very wide bandwidth multiband internal antennas that are compact.